During the past few years the occupant safety belt systems with which most vehicles have been equipped have employed emergency locking retractors, that is, retractors of the type that lock automatically in response to either abrupt acceleration of the belt in the unwinding direction or an abrupt acceleration of the vehicle, events that are most often associated with a vehicle collision. Emergency locking retractors have the advantage of allowing the user to lean forward in the vehicle rather than being strapped in with no opportunity for movement without undoing the belt. Moreover, they are, in general, easier to fasten up when the occupant enters the vehicle. They have been recognized as being entirely safe and effective. Some emergency locking retractors are constructed to respond to both acceleration of the belt and acceleration of the vehicle.
One problem with emergency locking retractors, and some other types of retractors as well, is that they permit a significant amount of elongation of the effective length of the belt in a collision due to the tightening of the several turns of the belt on the belt reel. Those turns or wraps of the belt that remain on the reel when it is fastened up are comparatively loose, and the very high forces imposed on the belt in a collision are sufficient to tighten those loops considerably, thereby allowing a length of the belt to withdraw from the belt reel even though the reel is locked against rotation by the emergency locking mechanism.
The inherent problem of emergency locking retractors of allowing some pull-out of the belt following locking of the retractor due to tightening of the loops that remain on the retractor is not particularly serious in the case of fixed belt systems, inasmuch as the number of turns of the belt that remain on the reel when the belt is fastened are comparatively small. On the other hand in some passive systems a significant number of turns remain on the belt when it is in the restraining configuration, those turns being required to enable the belt to be pulled out when it is transferred from the restraining to the releasing configuration. The greater number of comparatively loose turns of the belt on the reel increases the seriousness of the problem of belt elongation.
There have been various proposals for providing some sort of clamp in association with an emergency locking retractor to reduce or eliminate the release of a length of belt from the reel due to tightening of the remaining loops. Many of the proposals made in the past have been unsatisfactory either because they do not fully lock the belt but instead let it slip or they present the possibility of failure of the belt in the event of a very high pull-out force. There have also been belt clamps which seem adequate to withstand the pull-out force reasonably well without belt failure, but they have been difficult to release, an inconvenience for the occupant who has to release the belt by hand each time the device is activated.
The inventor of the present invention has heretofore invented the belt clamp shown in FIG. 1 of the accompanying drawings and described and shown more fully in U.S. patent application Ser. No. 107,161 filed Dec. 26, 1979 and entitled "Belt Clamps for Vehicle Passenger Restraint Belts" now U.S. Pat. No. 4,323,204. The belt clamp shown in FIG. 1 is intended to be used in conjunction with an emergency locking retractor, preferably by integrating the clamp in the same assembly and on the same U-shaped frame 10. The restraint belt B leads from the belt reel 12 of the retractor past a guide roll 14 and in between a fixed clamping jaw 16 strongly attached to the frame 10 and a movable clamp member 18 that normally falls by gravity into the position shown in solid lines in which it is spaced apart some distance from the fixed clamping jaw 16 so that the belt can run downward freely between the clamping jaws without touching either of them. The movable jaw 18 has a pair of laterally extending lugs 20, one extending laterally out at each end and each of which is received in an elongated guide hole 22. The belt B then turns part way around a corrugated turning roll 24 that is ordinarily held by springs 26 in a downward position. The force of the springs 26 is sufficient to keep the turning roll 24 in the downward position during normal unwinding and rewinding movements of the belt B but yields in the event of a relatively high pull-out force on the belt B, thereby moving upwardly to the position shown in phantom lines in FIG. 1 in which it engages the movable clamping jaw 18 and moves it into clamping engagement with the belt. The jaws have complementary corrugated clamping surfaces that provide a high frictional force that resists further pull-out of the belt B. The turning roll 24 is carried by a shaft 28, the ends of which extend outward into matching elongated holes 30 in the side members of the frame 10. The axes of the holes 30 establish a path of movement of the turning roll 24 that is generally aligned with the incoming segment of the belt B before it turns around the roll. The corrugated surface of the turning roll and the matching camming surface 18a of the movable clamping jaw provide for an increased transfer of forces in a direction transverse to the belt in response to the pull-out force on the belt, as compared to a plain cylindrical roll and a flat camming surface on the movable clamping jaw.
It will be understood by those skilled in the art that the emergency locking retractor 12 is shown schematically in FIG. 1. Such retractors have some sort of locking mechanism of either the belt pull-out sensitive or an inertia sensitive type, or both, as represented in FIG. 1 by a pendulum and pawl 32. A belt clamp constructed in accordance with the present invention can be used with any of a variety of types of emergency locking retractors.
Experiments conducted using belt clamps of a type shown in FIG. 1 have been successful in demonstrating the effectiveness of the use of a turning roll as a clamp actuating mechanism that, by camming action, urges a movable clamping jaw toward a fixed clamping jaw and causes the belt to be clamped between complementary corrugated clamping surfaces on the clamping jaws. Those experiments have, on the other hand, indicated a possible problem with the device shown in FIG. 1; if the belt is pulled off the turning roll 24 at an angle to one side or the other of a plane perpendicular to the axis of the shaft 28 of the turning roll, the forces transmitted from the turning roll to the movable clamping jaw are significantly higher at one side than they are at the other, thereby tending to produce an excessive clamping force on one side of the clamping jaws. The high force may be sufficient to initiate belt failure.